Bottom Line:
The diameter, settling velocity and SVI10 of granules ranged from 2 to 5 mm, 80 to 110 m/h and about 40 mL/g, respectively.Freezing microtome images, DO concentration profiles by microelectrode, distribution of bacteria and EPS by confocal laser scanning microscopy (CLSM) show that the aerobic granules have a three-layer structure.Each layer has different thickness, character, bacteria, and DO transfer rate.

Affiliation: College of Civil Engineering and Architecture, Zhejiang University of Technology, Hangzhou 310014, China. tanweilijun@zjut.edu.cn.

ABSTRACTAerobic granules were cultivated in a sequencing batch reactor (SBR). COD and ammonia nitrogen removal rate were 94% and 99%, respectively. The diameter, settling velocity and SVI10 of granules ranged from 2 to 5 mm, 80 to 110 m/h and about 40 mL/g, respectively. Freezing microtome images, DO concentration profiles by microelectrode, distribution of bacteria and EPS by confocal laser scanning microscopy (CLSM) show that the aerobic granules have a three-layer structure. Each layer has different thickness, character, bacteria, and DO transfer rate. A hypothesis for granule structure is proposed: the first layer, the surface of the granule, is composed mostly of heterotrophic organisms for organic matter removal, with a thickness range from 150 to 350 μm; the second layer, mostly composed of autotrophic organisms for ammonia nitrogen removal, with a thickness range from 250 to 450 μm; the third layer, located in the core of the granule, has mostly an inorganic composition and contains pores and channels.

ijerph-11-02427-f006: Equipotential line of DO microelectrode in the surface layer of a granule.

Mentions:
Figure 6 shows the equipotential lines of the DO microelectrode in the surface layer of a granule in water. The lines at different depth match with the profile of the granule surface. It indicates the first layer had a uniform structure.

ijerph-11-02427-f006: Equipotential line of DO microelectrode in the surface layer of a granule.

Mentions:
Figure 6 shows the equipotential lines of the DO microelectrode in the surface layer of a granule in water. The lines at different depth match with the profile of the granule surface. It indicates the first layer had a uniform structure.

Bottom Line:
The diameter, settling velocity and SVI10 of granules ranged from 2 to 5 mm, 80 to 110 m/h and about 40 mL/g, respectively.Freezing microtome images, DO concentration profiles by microelectrode, distribution of bacteria and EPS by confocal laser scanning microscopy (CLSM) show that the aerobic granules have a three-layer structure.Each layer has different thickness, character, bacteria, and DO transfer rate.

Affiliation:
College of Civil Engineering and Architecture, Zhejiang University of Technology, Hangzhou 310014, China. tanweilijun@zjut.edu.cn.

ABSTRACTAerobic granules were cultivated in a sequencing batch reactor (SBR). COD and ammonia nitrogen removal rate were 94% and 99%, respectively. The diameter, settling velocity and SVI10 of granules ranged from 2 to 5 mm, 80 to 110 m/h and about 40 mL/g, respectively. Freezing microtome images, DO concentration profiles by microelectrode, distribution of bacteria and EPS by confocal laser scanning microscopy (CLSM) show that the aerobic granules have a three-layer structure. Each layer has different thickness, character, bacteria, and DO transfer rate. A hypothesis for granule structure is proposed: the first layer, the surface of the granule, is composed mostly of heterotrophic organisms for organic matter removal, with a thickness range from 150 to 350 μm; the second layer, mostly composed of autotrophic organisms for ammonia nitrogen removal, with a thickness range from 250 to 450 μm; the third layer, located in the core of the granule, has mostly an inorganic composition and contains pores and channels.